The present invention relates to a carrier assembly which reduces damage associated with and is suitable for use in connection with packing, transporting and automatic insertion of Ceramic Pin Grid Array (CPGA) Modules.
Many complex integrated circuit chips have high Input/Output (I/O) requirements which Pin Grid Array (PGA) Modules satisfy. PGA modules have at least one chip mounting location on top of a substrate. The substrate is made of insulating material such as plastic for its low cost or ceramic for its thermal conductivity. A protective cap rigidly attached to the substrate encloses all chips mounted on the substrate. The protective cap may be made from the same material as the substrate, or from a different material such as metal. Each chip is mounted at a location which has a plurality of interconnect pads, with at least one interconnect pad for each chip input, each chip output, and each chip power pad. Some chip mounting locations may include additional Engineering Change (EC) pads for rerouting chip interconnects to make functional module changes and corrections or to fix partially bad chips. Most chip interconnect pads will be connected to other interconnect pads or to a termination point, or pin. A module with only one or two chips may be simple enough that all of the module wiring between interconnects and pins may be done on the top surface and the bottom surface of the substrate. A single layer of insulating material would separate the top wiring plane from the bottom wiring plane.
Alternatively, the substrate may have several parallel wiring planes, each plane insulated from adjacent wiring planes by insulating material. Such a substrate may also have wiring planes disposed on its top surface and its bottom surface. Interconnects or vias through an insulating layer connects wires on different wiring planes together. Thus, a signal path can meander from one side of the substrate to another, across several wiring planes to connect a chip interconnect pad on the top surface of the substrate and with a module pin at the bottom surface. A PGA module with multiple chips may have several wires between chips on the substrate for intra-module communication, i.e., where chips can communicate only with other chips on that substrate. However, chip I/O must communicate with other modules and are wired to module pins mounted on or in the bottom surface of the substrate. These substrate Pins form a Grid, densely arranged in an n by m Array, where n is the number of rows of pins and m is the number of columns. Thus, a module having such a substrate is called a PGA module.
A PGA module comprised of several complex integrated circuit chips and intricate intra-module wiring may be quite expensive. The actual cost of the material used to make the module is small. Substrate manufacturing, integrated circuit chip manufacturing, module assembly and testing costs account for most of the cost of the module. See U.S. Pat. No. 4,627,160 for an example of a process for making a multilayer ceramic substrate.
Module components and modules are tested at almost every stage of the module manufacturing process. Substrates are tested or "screened" for defects prior to mounting integrated circuit chips on them. Integrated circuit chips are mass produced on wafers the size of a dinner plate. A single rectangular chip may be replicated several hundred times on a single wafer. Each chip on a wafer is individually tested for manufacturing defects, or flaws, that occur at random wafer locations during almost every manufacturing step. Normally, an integrated circuit chip containing a defect is unusable. The tested wafer is cut up or "diced" into separate chips; the unusable chips are discarded and the good chips are mounted on substrates. These substrates with chips mounted on them, or "decks", are tested for defects which were introduced during chip mount. Any defective decks which can be repaired are then repaired and unrepairable decks are discarded. Decks that tested good or were repaired may then be "burned in", i.e., placed in operation for a short period to allow weak decks to fail. After burn in, the decks are retested. Any deck which tests good is capped; any deck which tests defective, but repairable, is repaired and capped. A capped deck which is a module. Each module may again be tested. Repairable modules are repaired and unrepairable modules are discarded. Good modules are shipped to a distributor and will eventually be assembled into a final assembly. A single microscopic crack in a substrate through a single signal wire would irreparably damage the substrate and render a tested module useless.
Accordingly, for protection, CPGA modules are typically shipped in plastic trays or in boxes which may be lined with protective foam. A substrate made of ceramic material is brittle like china. Although not as fragile as china, a ceramic substrate is breakable. Because ceramic substrates are breakable, even CPGA modules packed in plastic trays may be damaged. For example, a tray may be opened accidentally; the tray's contents spilled onto a hard floor; and some of the modules cracked or shattered. Similarly, by bumping one another in the tray, modules may fracture or chip each other, thus severing delicate substrate wiring. Still another type of damage that might occur is that module pins may be bent from being pushed into the protective foam or from being forced against other modules in the tray. Damage may result from mistreatment in handling when the modules are manually removed from the tray, hand carried to an assembly point, or manually inserted into a final assembly. Yet another type of handling damage occurs when static electricity is transferred to the module from a person touching the module. This type of damage, known as Electro Static Discharge (ESD) damage, may destroy the integrated circuit chip packaged in the CPGA module, while leaving the module exterior and substrate completely untouched and apparently fully functional.
Shipping tubes provide another means for shipping CPGA Modules. A shipping tube usually has a stopper in one end with CPGA packaged chips being slid into the opposite end. Once the tube is filled, a stopper inserted into the loading end keeps the modules in the shipping tube. However, prior art shipping tubes suffer many of the same limitations as packing trays. A CPGA module in a shipping tube is in constant contact with adjacent CPGA modules. So substrates of adjacent modules might be damaged by carelessly shaking the shipping tubes. As with shipping trays, the CPGA modules may be spilled if the stopper falls out of one end of the tube. Handling and ESD damage are just as likely to occur with shipping tubes as with shipping trays.
Some physical module damage may be easily discoverable because of bent pins, broken ceramic packages, or visible cracks in the ceramic. Often, however, module damage is either unnoticeable or nearly invisible. For example, ESD damage may destroy or impair a chip in a module without damaging the module package at all. Modules, thus invisibly damaged during shipping, may become part of a final assembly. Finding a bad chip in a complex assembly is much more difficult than finding a bad chip during module manufacture. Consequently, the expense of finding a defective module in a final assembly is much higher than the cost of finding a defective chip during module manufacture. As a result, companies are continually searching for ways to reduce the module damage which occurs between the point in time just prior to mounting chips in a module and the point in time when the modules are assembled into a final machine or onto a printed circuit card.
Traditional approaches taken to reduce ceramic package module damage include: Insertion of a flexible filler strip in a shipping tube such that the flexible filler strip rides above some of the ceramic modules in the shipping tube; Building of flexible bumpers onto the chip modules; Individually packaging ceramic modules in a protective carrier; and packing components in pockets molded into a plastic carrier tape, where the carrier tape is wound and stored upon a reel.
These approaches, however, still fail to provide adequate protection. For example, a flexible filler strip may hold some of the modules close to the end of the shipping tube firmly in place, but other modules in the tube can still bump one another and can thereby be damaged. Building bumpers onto the ends of the modules avoids the module bumping problem but, adds module manufacturing steps thereby increasing module manufacturing costs and manufacturing time. Individually packaging modules overcomes the bumping problem as well but, requires individual handling which, in addition to increasing costs, increases module exposure to handling related damage. Plastic tape carriers must be flexible enough to allow a tape, loaded with modules, to be wound upon a reel. This flexibility limits the protection afforded components carried in the tape and modules in the tape may still bump one another.